Geographically, Assam is located south of the eastern Himalayas situated between 8905/-960 1/ East Longitude and 2403/-27058/ North Latitude. It can be divided into three principal geographical regions: the Brahmaputra Valley in the north; the Barak Valley in the south; and the Karbi Anglong and Cachar Hills that divide the two regions with a total area of 30,285 square miles (78,440 km2). Assam is surrounded by six of the other Seven Sister States: Arunachal Pradesh, Nagaland, Manipur, Mizoram, Tripura, and Meghalaya. Assam is the sentinel of north-east India and gateway to the North-Eastern States. Assam also shares international borders with Bhutan and Bangladesh.
Assam has a stunning grandeur of dense tracts of tropical forests, interspersed with emerald patchwork quilts of paddy and lush tea gardens enriched by the flow of river Brahmaputra (‘Son of Brahma’).The northern part is wholly occupied by the elongated valley of the mighty Brahmaputra. Most of Assam’s population lives in this valley. The Brahmaputra valley is bounded by the foothills of the Himalayas to the north and another lower range of hills and mountains to the south.
In the center part of Assam, to the south of the hills is the Barak Valley which is contiguous with the densely populated country of Bangladesh. It is separated by the Karbi Anglong and North Cachar Hills from the Brahmaputra Valley in Assam. The Barak river originates from the Barail Range in the border areas of Assam, Nagaland and Manipur and flowing through the district of Cachar, it confluences with the Brahmaputra in Bangladesh. In the north there is North Cachar Hills, in the east there is Manipur Hills and in the south there is Mizoram hills.
Geomorphic studies conclude that the Brahmaputra, the life-line of Assam is an antecedent river, older than the Himalayas. The river with steep gorges and rapids in Arunachal Pradesh entering Assam, becomes a braided river (at times 10 mi/16 km wide) and with tributaries, creates a flood plain (Brahmaputra Valley: 50–60 mi/80–100 km wide, 600 mi/1000 km long). Main tributaries of Brahmaputra are Dikhow, Disang, Bhogdoi, Jhanji, Dhansiri, Jiya-Bharali, Burhi-Dihing, Suwonshiri, etc. Each and every year the flood generated by Brahmaputra and its tributaries, mainly because they receive heavy rainfall within a short time, seems to be one of the biggest problems of Assam. In the south, the Barak originating in the Barail Range (Assam-Nagaland border) flows through the Cachar district with a 40–50 km wide valley and enters Bangladesh with the name Surma.
Assam is endowed with petroleum, natural gas, coal, limestone and other minor minerals such as magnetic quartzite, kaolin, sillimanites, clay and feldspar. A small quantity of iron ore is available in western districts. Discovered in 1889, all the major petroleum-gas reserves are in Upper parts like Lakua, Rudrasagar, Geleki, etc.
Assam is one of the richest biodiversity zones in the world. There are a number of tropical rainforests in Assam. Assam is known for her rich forest wealth which constitutes 26.22 per cent of the total forest area. Moreover, there are riverine grass lands, bamboo orchards and numerous wetland ecosystems. Many of these areas have been protected by developing national parks and reserved forests. The Kaziranga and Manas are the two World Heritage Sites in the region. The Kaziranga is the home for the rare Indian Rhinoceros, while Manas is a tiger sanctuary.
With the “Tropical Monsoon Rainforest Climate”, Assam is temperate (summer max. at 95–100 °F or 35–38 °C and winter min. at 43–46 °F or 6–8 °C) and experiences heavy rainfall and high humidity. The climate is characterized by heavy monsoon downpours reducing summer temperatures and affecting foggy nights and mornings in winters. Rainfall in Assam ranks among the highest in the world; its annual rainfall varies from 70 inches in the west to 120 inches per year in the east. Spring (Mar–Apr) and autumn (Sept–Oct) are usually pleasant with moderate rainfall and temperature.
Assam is also prone to natural disasters. High rainfall, deforestation, and other factors which have resulted in annual floods. These often cause widespread loss of life, livelihood and property. The region is also prone to earthquakes: mild tremors are common, but strong earthquakes are rare. There have been three strong earthquakes: in 1869 the bank of the Barak sank by 15 ft. In 1897 there was a tremor which measured 8.1 on the Richter scale, and another in 1950 which measured 8.6.
Certificate Physical and Human Geography by Goh Cheng Leong.